This invention relates to techniques for electronically editing film.
Film video and audio source material is frequently edited digitally using a computer system, such as the Avid/1 Media Composer from Avid Technology, Inc., of Tewksbury, Mass., which generates a digital representation of a source film, allowing a film editor to edit the digital version, rather than the film source itself. This editing technique provides great precision and flexibility in the editing process, and is thus gaining popularity over the old style of film editing using a flatbed editor.
The Avid/1 Media Composer accepts a videotape version of a source film, created by transferring the film to videotape using the so-called telecine process, and digitizes the videotape version for editing via manipulation by computer. The operation of the Media Composer is described more fully in copending U.S. patent application Ser. No. 07/866,829, filed Apr. 10, 1992, now U.S. Pat. No. 5,355,450 and entitled xe2x80x9cMedia Composer with Adjustable Source Material Compression.xe2x80x9d The teachings of that application are incorporated herein by reference. Editing of the digitized film version is performed on the Media Composer computer using CRT monitors for displaying the digitized videotape, with the details being based on videotape timecode specifications. Once editing is complete, the Media Composer creates an edited videotape and a corresponding edit decision list (EDL) which documents the videotape timecode specification details of the edited videotape. The film editor uses this EDL to specify a cut and assemble list for editing the source film. While providing many advantages over the old style flatbed film editing technique, the electronic editing technique is found to be cumbersome for some film editors who are unaccustomed to videotape timecode specifications.
In general, in one aspect, the invention provides a system for generating a digital representation of a video signal comprised of a sequence of video frames which each include two video fields of a duration such that the video plays at a first prespecified rate of frames per second. The sequence of video frames includes a prespecified number of redundant video fields. In the invention, redundant video fields in the video frame sequence are identified by a video processor, and the video frame sequence is digitized by an analog to digital convertor, excluding the identified redundant video fields. The digitized video frames are then compressed by a video compressor to generate a digital representation of the video signal which plays at a second prespecified rate of frames per second.
In preferred embodiments the invention further provides for storing the digitized representation of the video signal on a digital storage apparatus. The redundant video fields are identified by assigning a capture mask value to each video field in the video frame sequence, the capture mask value of a field being a xe2x80x9c0xe2x80x9d if the field is redundant and the capture rusk value of a field being a xe2x80x9c1xe2x80x9d for all other video fields. A video frame grabber processes the video frame sequence based on the capture mask values to exclude the identified redundant video frames from being digitized. The video compressor compresses the video frames based on JPEG video compression.
In other preferred embodiments, the first prespecified video play rate is 29.97 frames per second and the second prespecified digital video play rate is 24 frames per second. The rate of the analog video signal is increased from 29.97 frames per second to 30 frames per second before the step of digitizing the video frame sequence. In further preferred embodiments, the analog video signal is a video representation of film shot at 24 frames per second, and the digital video play rate of 24 frames per second corresponds to the 24 frames per second film shooting rate. The analog video signal is a representation of film that is transferred to the video representation using a telecine apparatus.
In general, in another aspect, the invention provides an electronic editing system for digitally editing film shot at a first prespecified rate and converted to an analog video representation at a second prespecified rate. The editing system includes analog to digital converting circuitry for accepting the analog video representation of the film, adjusting the rate of the analog video such that the rate corresponds to the first prespecified rate at which the film was shot, and digitizing the adjusted analog video to generate a corresponding digital representation of the film. Further included is a digital storage apparatus for storing the digital representation of the film, and computing apparatus for processing the stored digital representation of the film to electronically edit the film and correspondingly edit the stored digital representation of the film.
In preferred embodiments, the system further includes digital to analog converting circuitry for converting the edited digital representation of the film to an analog video representation of the film, adjusting the rate of the analog video from the first prespecified rate to the second prespecified video rate, and outputting the adjusted analog video. Preferably, the analog video representation of the film accepted by the analog to digital converting circuity is an NTSC videotape. The apparatus for storing the digital representation of the film also stores a digitized version of a film transfer log corresponding to the digital representation of the film. The system includes display apparatus for displaying the digitized version of the film as the film is electronically edited and displaying a metric for tracking the location of a segment of the film as the segment is displayed, the metric being based on either film footage code or video time code, as specified by the system user.
The electronic editing system of the invention allows users to provide the system with film formatted on standard videotapes, NTSC tapes, for example, and yet allows the video to be digitally edited as if it were film, i.e., running at film speed, as is preferred by most film editors. By reformatting the analog video as it is digitized, the system provides the ability to electronically edit film based on the same metric used in conventional film editing.